In Escherichia coli arginine plus the arginine-regulatory protein, argR, act in concert to control both arg-messenger RNA levels and enzyme synthesis throughout all six arginine operons (the arginine regulon). It is the purpose of the proposed research to determine the relative importance of early-termination control and initiation control of arg mRNA synthesis in the regulation of expression of the argECBH cluster in E. coli. Experiments are designed to determine more exactly the origin and regulation of the formation of short versus long argECBH mRNA species. Studies are proposed to distinguish the suspected dual roles of the arginine-argR protein complex in regulation of argECBH mRNA synthesis. In addition, the role of the arginyl-tRNAarg system and other cellular factors in regulation of early termination will be investigated.